Assessment of phenol compound removal from olive oil mill wastewater by using peroxidases extracted from radish and nettle leaves

The aim of this work is to evaluate the degree of degradation phenolic compounds in olive mill wastewater (OMW), using crude plant peroxidases. In fact, OMW was treated with crude peroxidases extracted from radish (Raphanus sativus L.) and nettle (Urtica urens L.) leaves. A significant reduction of more than 60% of total phenols was observed in OMW incubated with peroxidase crude extract during seven days. The present chromatographic data obtained by high performance liquid chromatography (HPLC) show that enzymatic treatment may change the composition of the polyphenols contained in the OMW. Thus, we observed a significant decrease in some phenolic acid levels, such as gallic acid, p-coumaric acid and hydroxytyrosol, and the disappearance of vanillic acid, compared to the non-treated OMW. Finally, phytotoxicity of the treated and non-treated OMW was tested by means of young sunflower plants (Helianthus annuus) grown in hydroponic medium. Our results showed that sunflower plants grow normally when the nutrient medium contains treated OMW; whereas they fade rapidly in the presence of non-treated OMW. We conclude that treatment of OMW with radish and nettle crude extracts could attenuate OMW phytotoxicity considerably.

Generation of lignin polymer models via dehydrogenative polymerization of coniferyl alcohol and syringyl alcohol via several plant peroxidases involved in lignification and analysis of the resulting DHPs by MALDI-TOF analysis

The mechanism of lignin dehydrogenative polymerization (DHP), made by means of horseradish peroxidase (HRP), was studied in comparison with other plant peroxidases. Interestingly, HRP is efficient for guaiacyl type polymer formation (G-DHPs), but is not efficient in the case of syringyl type DHPs (S-DHPs). It was previously demonstrated that lignification-relatedArabidopsisthalianaperoxidases, AtPrx2, AtPrx25 and AtPrx71, and cationic cell-wall-bound peroxidase (CWPO-C) fromPopulus albaare successful to oxidize syringyl- and guaiacyl-type monomers and larger lignin-like molecules. This is the reason why in the present study the DHP formation by means of these recombinant peroxidases was tested, and all these enzymes were successful for formation of both G-DHP and S-DHP in acceptable yields. CWPO-C led to S-DHP molecular size distribution similar to that of isolated lignins.